1. Field of the Invention
The present invention relates to a switching power supply, and particularly to a soft-start technique for gradually raising the output voltage of the switching power supply.
2. Description of the Related Art
In order to convert a DC voltage having a given voltage level to a DC voltage having a different voltage level, a switching regulator (DC/DC converter) is employed. Such a switching regulator includes a switching element, a rectifier element, an inductor, and an output capacitor. The switching regulator is configured to stabilize the output voltage to a desired voltage level by adjusting the duty ratio of the on/off operation of the switching element.
When starting up the switching regulator, there is a need to raise the output voltage from a 0 V state, i.e., a state in which the amount of charge stored in the output capacitor is zero, to a state in which it reaches a target value. If there is a sudden increase in the output voltage, in some cases, this leads to an inrush current occurring in the output capacitor, or leads to overshoot or ringing occurring in the output voltage, which excessively raise the output voltage. In some cases, this leads to adverse effects on the reliability of the circuit elements.
Accordingly, in order to prevent such an inrush current from occurring, a soft-start circuit is provided to such a switching regulator. Such an arrangement performs a soft-start control operation so as to gradually increase the output voltage.